The technology of drum drying wet synthetic surfactant materials is old. Sodium alkyl benzene sulfonate (LAS) is a notoriously hygroscopic material. Substantially pure LAS flakes are tacky. Sodium alkyl sulfate (AS) flakes are free flowing and have noncaking properties. Mixtures or co-flakes of AS/LAS have varying physical properties.
U.S. Pat. No. 4,253,993, J. C. Ramsey and P. J. Schoner, issued Mar. 3, 1981, for Shampoo in Flake Form, discloses a process comprising drum drying an aqueous slurry of 45-75% sodium alkyl sulfate (AS), monoethanol amide (MEA), sodium sulfate to make a flake containing 40-60% AS, 2-5% MEA and 20-50% sodium sulfate. Although other drying techniques are disclosed, this patent does not teach the use of nitrogen or dry air to cool the drum dried flakes. U.S. Pat. No. 3,950,275, Toyoda et al., issued Apr. 13, 1976, discloses the use of a coating of builders to stabilize spray dried granules of hygroscopic LAS detergent compositions. This patent is cited to show the state of the art.
In the food art low humidity cooling of drum dried food flakes is known. The following references are examples. "Improved drum-dried tomato flakes are produced by a modified drum dryer" which employs low humidity collection zones. M. E. Lazar and J. C. Miers, August, 1971. Food Technology, Vol. 25, p. 830. "Secondary drying of drum-dried thermoplastic foods," M. A. Lazar and T. Rumsey, 1976, J. of Food Sci., Vol. 41, p. 696, is another reference. United Kingdom Pat. Appln. No. 2,083,188, J. F. Fuller, Mar. 17, 1982, discloses that a puree of fresh fruit is dried on a drum to produce flakes, the whole process being carried out under dehumidified atmospheric conditions.
The above prior art does not teach stabilizing drum dried hygroscopic AS/LAS surfactant flake compositions with dry air or nitrogen. Nor does the prior art teach that such AS/LAS coflakes can carry more perfume in solid cake compositions than cakes made with either AS or LAS flakes alone, or AS/LAS coflakes cooled in an environment having a dewpoint over 10.degree. C.
This invention relates to surfactant flakes which can be used to make surfactant cake compositions which are used in automatic dispensing devices. Examples of such cakes are disclosed in U.S. Pat. No. 4,308,625, Kitko, issued Jan. 5, 1982; U.S. Pat. No. 4,310,434, Choy and Greene, issued Jan. 12, 1982; and U.S. Pat. No. 4,278,5671, Choy, issued July 14, 1981, entitled "Surfactant Cake Compositions". The surfactants provide sudsing in the toilet bowl and also serve to disperse other components of the compositions such as dyes, perfumes, organic resins, etc. Anionic surfactants, especially the organic sulfates and sulfonate types, are used in these compositions because of their availability, low cost and dispensing properties.
Water-soluble inert salts such as alkali metal chlorides and sulfates are used in such compositions to act as a "filler" so that the composition can be formed into cakes of desirable size without using excessive amounts of active ingredients. The predominant ingredients of the cake compositions are usually the surfactant, perfume and the filler salt. Anionic, nonionic, zwitterionic or cationic surfactants are used. The surfactant or surfactant mixture should be solid at temperatures up to about 100.degree. F. (40.degree. C.). Anionics and nonionics and mixtures thereof are useful. Anionics are the most preferred.
The prior art anionic surfactant cakes can be described as essentially the water-soluble alkali metal salts, of organic sulfuric reaction products having in their molecular structure an alkyl or an alkylaryl radical containing from 8 to 22 carbon atoms.
A major problem in this art has been short and/or erratic longevity of surfactant cakes. Another problem is related to the incorporation of higher levels of perfume into surfactant cake formulations while maintaining desired firmness.